By 10 a.m. local time, the Civic Center area bounded by First Street, Temple Street and Judge Aiso had been closed to all motor-vehicle traffic. Most office workers in the area were told to go home for the day and call back this afternoon to see if they would be allowed to return Tuesday morning.

A spokesman for the Los Angeles Police Department said the security moves were "not indicative" of any specific threats by terrorists against LA, but rather a "precautionary move to protect against retaliatory attacks" that some experts believe will be made against major US cities in the wake of the military action taken in Afghanistan.

Though traffic in Downtown LA was more snarled than usual because of the blockades, it could have been worse: Many government workers didn't even have to report to work this morning because it's Columbus Day, a holiday for many federal and state employees. Law-enforcement officials are telling government and private-sector workers alike to prepare for even more delays Tuesday and make sure they carry at least one—and preferably two—forms of identification to make it through the heightened security.